In the past, plastic fittings have been used for receiving a threaded male part, typically a threaded pipe. Also, in the past, reinforcing rings have been used to reinforce plastic fittings, such as described in U.S. Pat. Nos. 5,582,439 and 6,866,305 to Spears and U.S. Patent Application 2004/0051316 to Spears. Also, U.S. Pat. No. 4,682,797 to Hildner and U.S. Pat. No. 6,186,558 to Komolrochanapom, as well as U.S. Patent Application 2003/0184085 to Thompson, disclose a reinforcing ring used with plastic fittings.
Although reinforcing rings that have been made in the past, and used with plastic fittings, there have been problems with such rings and fittings, particularly relating to cross-threading and shearing. Therefore, the present invention provides an improved reinforcing ring and an improved fitting incorporating the reinforcing ring.
One problem is that when the male part which is being inserted into the plastic fitting is over-tightened, there is a tendency for the plastic fitting to shear.
Also, cross-threading occurs when the thread axis of the male part is not properly aligned relative to the female fitting's thread axis. All plastic thread design is susceptible to cross-threading. One way of at least reducing the risk of cross-threading is to guide the male part to be axially in line with the female fitting. Another way to lessen the likelihood of cross-threading is to reinforce the first few plastic threads of the fitting with a harder material. The present invention has been able to successfully combine both of these approaches to provide an improved method of reducing the likelihood of cross-threading using only a single starter thread. None of the prior art reinforcing rings use only a single starter thread.